Photographic capsular products



United States Patent Oflice 3,396,026 Patented Aug. 6, 1968 3,396,026PHOTOGRAPHIC CAPSULAR PRODUCTS Lloyd D. Taylor, Everett, Mass., assignorto Polaroid Corporation, Cambridge, Mass., a corporation of Delaware NoDrawing. Filed Mar. 25, 1963, Ser. No. 267,847 9 Claims. (Cl. 96-94)ABSTRACT OF THE DISCLOSURE This invention relates to microscopiccapsules having walls which include a substantially continuous polymericlayer comprising a coacervate containing a low isoelectric point gelatinand a gelatin derivative, which derivative comprises the reactionproduct of gelatin and a derivatizing agent which reacts with at least aportion of the gelatins amino groups, surrounding a nucleus comprising awater-immiscible medium and which are adapted to retain materialssuitable for use in photographic black and white and color processes.

The copending application of William J. McCune, Jr., filed May 9, 1961,Ser. No. 108,774, now Patent 3,276,- 869, discloses the use of minutecapsules for use in photographic processes. In one embodiment, theminute capsules contain dye developers for use in preparing color imagesby the diffusion transfer process. In another embodiment, themicroscopic capsules are coated with a layer of silver halide. U.S.Patent No. 2,983,606, issued May 9, 1961, to Howard G. Rogers, disclosesprocesses employing dye developers to form color transfer images andproducts useful therein. The copending application of Edwin H. Land andHoward G. Rogers, Ser. No. 565,135, filed Feb. 13, 1956, discloses theuse of such dye developers in integral multilayer negatives to givemulticolor transfer images.

Accordingly, it is one object of this invention to provide novel minutecapsules for use in the photographic products and processes.

Another object of this invention is to provide minute capsules whosewalls comprise photographic gelatin.

Still another object of this invention is to provide capsules whosewalls comprise gelatin and photosensitive silver halide.

Still another object of this invention is to provide novel processes forthe preparation of minute capsules.

Still another object of this invention is to provide capsules of theaforementioned structure wherein colorproviding materials areencapsulated.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others, and the product possessing the features,properties and the relation of elements which are exemplified in thefollowin detailed disclosure, and the scope of the application of whichwill be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description.

Methods of preparation of microscopic, pressurerupturable capsulescontaining a water-immiscible medium are well known to the art.Generally, such capsules are formed by deposition of a complex colloidmaterial around microscopic droplets of a water-immiscible medium by theprocess of causing coacervation, by dilution or adjustment of the pH, tooccur in a mixture of two different colloid salts in which theWater-immiscible material is dispersed as droplets, and then gelling thecomplex colloid. Generally, a complex colloid material is forme of anaqueous solution of one colloid, emulsifying the nuclei material orinternal phase therein and mixing the thus-formed emulsion with anaqueous salt of another colloid. Alternatively the two colloid materialsmay be made and mixed and the water-immiscible material emulsifiedtherein. Coacervation is then brought about by dilution and/or byadjusting the pH of the mixture. The gellable colloid materials used inthe solutions must be ionizable and the art has taught that the solsmust exist in the mixture with opposite electric charges. One wellknownsystem comprises high isoelectric point gelatin as the positive colloid,gum arabic as the negative colloid, and water. A solution of thesematerials is prepared and the pH and concentration of the system isadjusted to a point where coacervation occurs. A water-immisciblematerial may then be added to the solution and the gelatin-gum arabiccoacervate phase will deposit around the water-immiscible dropletsthereby encapsulating the water-immiscible medium.

In photographic products and processes, low isoelectric point gelatin ispreferred as a colloid binder over higher isoelectric point gelatin.Accordingly, it becomes considerably more desirable to prepare minutecapsules which are to be used in photographic products and processeswith low isoelectric point gelatin. Also, gum arabic is not availabledomestically and problems of supply may arise. Therefore, the problemthat presents itself is to replace a positive colloid with a negativecolloid and still pro vide a system in which a coacervate can be formed.

The novel process of this invention comprises encapsulation ofwater-immiscible materials in low isoelectric point gelatin,particularly photographic grade gelatin, to form minute capsules.

In one embodiment of the present invention, the encapsulating wallmaterial comprises low isoelectric point gelatin and, as a secondcolloid material, a gelatin derivative comprising the reaction productof a dicarboxylic acid anhydride and gelatin.

In carrying out the novel process of this invention, a solution of lowisoelectric point gelatin is prepared and a solution of a second colloidis added. With constant stirring throughout, the temperature and pH ofthe system is adjusted to provide a coacervate phase of the gelatin andthe second colloid. The water-immiscible internal phase material is thenadded to the coacervate and the solution is cooled slowly. Capsules areformed by the deposition of the complex colloid comprising gelatin andthe second colloid around the droplets of the internal phase. Thecapsular Walls are also hardened by the lowering of the temperature. Thethus-formed capsules may then be hardened by appropriate means, forexample, rapid cooling and/ or the addition of the hardening agent suchas glutaraldehyde. The hardened capsules may then be isolated and driedand utilized in the desired appropriate manner.

As examples of suitable dicarboxylic acid anhydrides which may bereacted with gelatin to form gelatin derivative reaction products,mention may be made of phthalic anhydride, tri-mellitic anhydride,succinic anhydride and glutaric anhydride. The type of gelatin which isreacted with the dicarboxylic acid anhydride is not critical; high orlow isoelectric point gelatin may be used. It should be noted, however,that certain anhydrides are known which will cross-link gelatin.Therefore, these materials should be avoided when selecting anhydridesto prepare a gelatin product for use as the second colloid in thisinvention. Gelatin-anhydride reaction products are prepared according tothe procedure set forth in U.S. Patent No. 2,525,753.

It should be understood that the dicarboxylic acid anhydrides suitablefor use in this invention may have other carboxylic acid groups as wellas the two that make up the anhydride groups.

It should be understood that while gelatin derivatized with dicarboxylicacid anhydrides is one of the preferred materials for use as the secondcolloid gelatin derivatized with other materials which will react withthe amino groups of the gelatin is also useful provided that carboxylicacid groups are also added to the gelatin. For example, gelatinderivatized with pcarboxybenzenesulfonyl chloride may also be suitablefor use in this invention as the second colloid.

It has also been found that minute capsules containing photosensitivesilver halide salts in the capsule walls can be prepared by the novelprocess of this invention. The aforementioned capsules comprise gelatinwith silver halide deposited therein encapsulating an internal phasematerial. Gelatin-silver halide capsules may be prepared by forming acoacervate of a solution of gelatin-silver halide emulsion and a secondcolloid, such as the reaction product of gelatin and a dicarboxylic acidanhydride in accordance with the above-disclosed procedure.

The gelttin-silver halide emulsion is prepared by procedures well knownto the art, for example, by reacting a water-soluble silver salt,preferably silver nitrate, with at least one water-soluble halide salt,preferably sodium or potassium bromide, most preferably in combinationwith sodium or potassium iodide, in an aqueous solution of a lowisoelectric point gelatin colloid peptizing agent. Additionalpreparation and sensitization may be carried out by any of the acceptedprocedures known to the art.

The terms sensitive, photosensitive and sensitized and other terms ofsimilar import are herein employed in the generic sense to describematerials possessing physical and chemical properties which enable themto form usable images when exposed to actinic radiation.

By means of the above-described novel process of this invention, solidsas well as solutions and suspensions may comprise the internal phase.Solid materials may then be encapsulated by three methods: (1) by directencapsulation of a solid, (2) by the encapsulation of a solution of thesolid in a volatile solvent, and evaporating the solvent after theformation of the capsule, thereby leaving the solid inside, and (3) bythe encapsulation of the solid suspended in a material, preferably anorganic solvent which is also immiscible in the aqueous coacervatesystem.

The following nonlimiting examples illustrate the preparation ofcapsules within the scope of this invention.

Example 1 The pH of 173 ml. of 8% aqueous solution of the reactionproduct of gelatin and phthalic anhydride (prepared according to themethod disclosed in U.S. Patent No. 2,525,753) was adjusted to a pH of6.5 and added to 700 ml. of water at 45 C. 200 ml. of a 10% aqueoussolution of low isoelectric point gelatin was adjusted to a pH of 6.5and added to the gelatin derivative solution. The pH of the combinedsolution was then adjusted to 4.5 with acetic acid. 190 ml. of toluenewas then added to the solution with vigorous agitation and the mixturewas then allowed to cool gradually to about 25 C. The temperature of thesolution was then dropped rapidly to 10 C. with a Dry Ice acetone bath.10 ml. of glutaraldehyde was then added to the solution and the capsuleswere isolated and dried.

It should be noted that the gelatin-silver halide mixture must be in theform of an emulsion prior to the addition of the second colloid in orderto insure that the silver halide will be present in the walls of thecapsules. For example, if silver halide were added to a solution ofgelatin and capsule preparation carried out, the silver halide itselfwould be encapsulated as the internal phase but would not be present toany extent in the capsule wall. It should be noted further that thepresent invention provides silver halide to the capsule walls in thesame operation that prepares the capsules themselves and that the silverhalide is a component part of the wall, whereas the above-mentionedcopending application, Serial No. 108,- 774, discloses a separate layerof silver halide deposited on the wall of the capsule after the capsulehas been prepared.

The copending application of Lloyd D. Taylor, Ser. No. 267,838, filedMar. 25, 1963, discloses and claims minute capsules whose walls comprisea single colloid material. It should be understood that a photosensitivesilver halide emulsion can be prepared utilizing said single colloid andthe thus-prepared colloid can be used in the preparation of capsuleswhich contain silver halide in the capsular walls accordingv to theprocedure of the above-noted copending application Ser. No. 267,838,filed Mar. 25, 1963.

In preparing capsules by the novel process of this invention, theagitation or stirring action given the colloid system is determinativeof the size of the droplets of water immiscible phase and ultimately thesize of the capsules. The more vigorous the stirring action, the smallerthe size of the droplet. For example, capsules about 1 to 10 microns insize may be prepared using the stirring action of a Waring Blcndor.Larger size capsules would be prepared by less vigorous stirring action.Capsules prepared by the novel process of this invention are in the 1 tomicron range.

The complex colloid system in this invention utilizes what isessentially two negative colloids at an acid pH. The difference incharge between the colloids is one of degree, not kind.

The novel capsules prepared by the process of this invention whichcontain color-providing substances or which comprise walls of gelatincontaining photosensitive silver halide are useful in photographicproducts and processes. For example, such capsules may be used inphotosensitive elements disclosed in the above-mentioned copendingapplication, Ser. No. 108,774. It should be understood that, inphotographic applications, the internal phase may be extracted from thecapsules by an aqueous alkaline solution. Capsules within the scope ofthe present invention may also be used in printing or reproductionsprocesses. For example, a dye or printing oil may be incorporated intothe internal phase prior to coacervation and a layer of the capsulesprinted on a sheet of paper. By the application of pressure in aparticular pattern, the capsules will rupture liberating the dye or oilthus reproducing the original pressure pattern on the paper.

Since certain changes may be made in the above prodnets and processeswithout departing from the scope of the invention herein involved, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

I claim:

1. A process of making microscopic capsules which comprises, incombination, the steps of (1) providing a fluid mixture which comprisesan aqueous solution of a low isolelectric point gelatin and a gelatinderivative, said gelatin derivative comprising the reaction product ofgelatin and a gelatin derivatizing agent which reacts with at least aportion of the amino groups of gelatin to provide neutralization of atleast a portion of the positive charges provided to the gelatinmolecule, in aqueous solution, by said amino groups, at least one ofsaid gelatin and said gelatin derivative having associated therewith adispersion of photosensitive silver halide, and a water'immisciblemedium, whereby droplets of said water-immiscible medium are provideddispersed in said aqueous solution;

(2) adjusting the pH and temperature of the fluid mixture to causecoacervation of said gelatin and said derivatized gelatin, whereby saidcoacervate deposits around the individual droplets of saidwater-immiscible medium, individually encapsulating said droplets;

(3) gelling said coacervate by cooling said capsules below the gellingtemperature of said coacervate.

2. The process as defined in claim 1 wherein said gelatin derivatizingagent comprises a dicarboxylic acid anhydride.

3. A process as defined in claim 1 wherein said waterimmiscible mediumcomprises a dye developer.

4. A process of making microscopic capsules which comprises, incombination, the steps of:

(1) providing a fluid mixture which comprises an aqueous solution of alow isoelectric point gelatin and a gelatin derivative, said gelatinderivative comprising the reaction product of gelatin and a gelatinderivatizing agent which reacts with at least a portion of the aminogroups of said gelatin to provide neutralization of at least a portionof the positive charges provided to the gelatin molecule, in aqueoussolution, by said amino groups, and a water-immiscible medium comprisinga dye developer, whereby droplets of said water-immiscible medium areprovided dispersed in said aqueous solution;

,(2) adjusting the pH and temperature of the fluid mixture to causecoacervation of said gelatin and said derivatized gelatin, whereby saidcoacervate deposits around the individual droplets of saidwater-immiscible medium, individually encapsulating said droplets;

(3) gelling said coacervate by cooling the capsules below the gellingtemperature of said coacervate.

5. Microscopic capsules comprising a substantially continuous polymericlayer surrounding a nucleus comprising a water-immiscible medium, saidpolymeric layer comprising a coacervate containing a low isoelectricpoint gelatin and a gelatin derivative which comprises the reactionproduct of gelatin and a gelatin derivatizing agent which reacts with atleast a portion of the amino groups of gelatin to provide neutralizationof at least a portion of the positive charges provided to the gelatinmolecule,

in aqueous solution, by said amino groups, at least one of said gelatinand said gelatin derivative having associated therewith a dispersion ofphotosensitive silver halide.

6. A product as defined in claim 5 wherein said gelatin derivatizingagent comprises a dicarboxylic acid anhydride.

7. A product as defined in claim 5 wherein said waterimmiscible mediumcomprises a dye developer.

8. Microscopic capsules comprising a substantially continuous polymericlayer surrounding a nucleus comprising a water-immiscible dye developer,said polymeric layer comprising a coacervate containing 'a lowisoelectric point gelatin and a gelatin derivative which comprises thereaction product of gelatin and a gelatin derivatizing agent whichreacts with at least a portion of the amino groups of gelatin to provideneutralization of at least a portion of the positive charges provided tothe gelatin molecule, in aqueous solution, by said amino groups.

9. A product as defined in claim 8 wherein said gelatin derivatizingagent comprises a dicarboxylic acid anhydride.

References Cited UNITED STATES PATENTS 2,728,662 12/1955 Yutzy et al.9694 2,800,457 7/1957 Green et al. 252-313 2,843,489 7/ 1958 Wilson etal. 9698 2,870,012 1/1959 Godowsky et al. 9697 3,000,740 9/ 1961 DeBelder et al. 9694 3,001,873 9/1961 Foris 9629 3,328,257 6/1967 Vranckenet al. 16783 FOREIGN PATENTS 221,880 5/ 1959 Australia.

NORMAN G. TORCHIN, Primary Examiner.

I. P. BRAMMER, Assistant Examiner.

